1. Field of the Invention
The present invention relates to an instant film pack incorporating peel-apart type instant film units.
2. Description of the Related Art
Presently available self-developing instant film units include, besides those of mono-sheet type, peel-apart type film units which have conventionally been used. A peel-apart type instant film unit (hereinafter referred to simply as the film unit) includes a photosensitive sheet and an image-receiving sheet which are joined by a connecting sheet. A plurality of such film units are stacked in layers and accommodated in a container to form a film unit assemblage, or a film pack, wherein photosensitive sheets and image-receiving sheets are separately layered so that they are located on two opposite sides inside the film pack. When one film unit is withdrawn from the container by pulling a leader sheet of the film unit after exposure, the photosensitive sheet and the image-receiving sheet connected contiguously to the leader sheet superposed face to face and pass between a pair of developer spreading rollers. As the film unit is pulled out in this fashion, the rollers rupture a developer solution pod retaining a viscous developer solution and spread the developer solution between the photosensitive sheet and the image-receiving sheet.
An image frame sheet (hereinafter referred to also as the mask) is detachably mounted on the image-receiving sheet and a pair of spacers(hereinafter referred to also as the rails) are attached to both side edges of the mask along which the image-receiving sheet is withdrawn. The spreading width of the viscous developer solution packed in the developer solution pod is determined by the distance between the two spacers, while the thickness of the spread developer solution is determined by the total thickness of the mask and the rail.
The connecting sheet and the image frame sheet may be separate or may be formed contiguously.
The developer solution pod holds a somewhat excess amount of developer solution to make it possible to spread the developer solution with a uniform thickness and prevent insufficient spreading of the developer solution due to a shortage thereof. A remnant portion of the viscous developer solution left over after it has been spread over an area of specified image frame is carried to and trapped in an area between developer solution trapping chips (hereinafter referred to also as the solution trapping chips) which is provided next to the spacers. Since the developer solution trapping chip has a trapezoidal or semicircular cross section and its height is several times larger than the total thickness of the mask and the rail, the thickness of the developer solution spread in the area between the solution trapping chips is also several times larger than the thickness of the developer solution spread in the area within the image frame. As a consequence, the developer spreading length in the former area is shortened by a factor of several times so that the developer solution would leak in no case from the film unit.
FIG. 1 shows the structure of a conventional container 2 of a film pack used for accommodating peel-apart type film units. The container 2 comprises an upper case section 4 constituting an upper face of a rectangular parallelepiped-shaped box-like case, a bottom cover 6 covering a bottom opening of the upper case section 4 and constituting a bottom face of the case, and a film pressure plate 5 located between the upper case section 4 and the bottom cover 6. An exposure opening 3 is formed in the upper case section 4 as illustrated. The lower edge of a leading end wall 7 of the upper case section 4 is located above the lower edges of side walls of the upper case section 4, so that there is formed a film unit exit immediately beneath the leading end wall 7 when the bottom cover 6 is fitted to the upper case section 4 to close its bottom opening.
FIG. 2 is cross-sectional view of the film pack as it is accommodated in a holder. Photosensitive sheets 40 and image-receiving sheets 41 of multiple peel-apart type film units are separately stacked and positioned above and beneath the film pressure plate 5 inside the film pack container 2. The film pack is provided with a light-shielding sheet 42 in unused state for closing the exposure opening 3. While the film pack container 2 usually contains approximately ten film units, only one film unit is depicted in FIG. 2 together with the light-shielding sheet 42 for the sake of simplification of the drawing. FIG. 2 shows that the photosensitive sheet 40 is located above the film pressure plate 5, facing the exposure opening 3, and that the image-receiving sheet 41 is positioned underneath the film pressure plate 5, wherein the photosensitive sheet 40 and the image-receiving sheet 41 are joined together by the connecting sheet 47.
FIG. 3 shows the structure of a conventional film unit 10. The film unit 10 is constructed such that, when a leader sheet 43 is withdrawn, by means of the connecting sheet 47 connected contiguously to the leader sheet 43, a photosensitive sheet 40 and an image-receiving sheet 41 are superposed face to face and caused to pass through a pair of developer spreading rollers 25.
More specifically, when a user pinches and pulls the leader sheet 43 projecting from between the developer spreading rollers 25, the photosensitive sheet 40 is caused to move leftward (as illustrated in FIG. 2), turn upside down at a curved portion 13 of a film pressure plate 5, and advance to the bottom side of the film pressure plate 5 with an exposed face of the photosensitive sheet 40 facing down. As the film unit 10 is withdrawn in this fashion, a developer solution pod 46 attached to the reader sheet 47 passes over the image-receiving sheet 41 and moves toward the developer spreading rollers 25. When the connecting sheet 47 interconnecting the image-receiving sheet 41 and the leader sheet 43 is fully stretched, the exposed face of the photosensitive sheet 40 is superposed with the image-receiving sheet 41. When the film unit 10 is further withdrawn by pulling the leader sheet 43, the photosensitive sheet 40 and the image-receiving sheet 41 together move toward the developer spreading rollers 25 superposed in superposed relationship.
Immediately before the developer solution pod 46 passes between the developer spreading rollers 25, the developer solution pod 46 is ruptured. As the film unit 10 is further withdrawn, developer solution packed in the developer solution pod 46 is spread with a uniform thickness between the photosensitive sheet 40 and the image-receiving sheet 41.
FIG. 4 is an enlarged perspective view of the image-receiving sheet 41. An image frame sheet 83 is detachably mounted on the image-receiving sheet 41 and a pair of spacers 81 are attached to both side edges of the image frame sheet 83 along which the image-receiving sheet 41 is withdrawn. A pair of developer solution trapping chips 82 are provided at trailing end areas of the rails 81 as illustrated. As the film unit 10 is pulled by its leader sheet 43, a remnant portion of the developer solution left over after it has been spread over a specified image frame area is carried to and trapped in an area just before the developer solution trapping chips 82. Therefore, the developer solution would not leak to the exterior when the film unit 10 is withdrawn from a holder. After the film unit 10 has been fully pulled out from between the developer spreading rollers 25, the film unit 10 is left until specific developing and fixing time elapse. When this waiting time has elapsed, a positive image appears on the image-receiving sheet 41. A finished photographic print is obtained when the image-receiving sheet 41 is peeled off from the film unit 10.
Polyvinyl chloride has conventionally been used for making the developer solution trapping chips since they are produced by first forming a continuous chip blank by contour extrusion and then cutting it into a desired size. Polyvinyl chloride is slow to set in contour extrusion process and is difficult to handle due to its tendency to deform when wound on a reel in the form of a continuous shape. Furthermore, the continuous shape of polyvinyl chloride produces a large amount of swarf in cutting operation.